Military branches:
United States Armed Forces: US Army, US Navy (includes Marine Corps), US Air Force, US Coast Guard; note - Coast Guard administered in peacetime by the Department of Homeland Security, but in wartime reports to the Department of the Navy (2013)

Military service age and obligation:
18 years of age (17 years of age with parental consent) for male and female voluntary service; no conscription; maximum enlistment age 42 (Army), 27 (Air Force), 34 (Navy), 28 (Marines); service obligation 8 years, including 2-5 years active duty (Army), 2 years active (Navy), 4 years active (Air Force, Marines); DoD is eliminating prohibitions restricting women from assignments in units smaller than brigades or near combat units (2013)

Military expenditures:
4.35% of GDP (2012) 4.75% of GDP (2011) 4.35% of GDP (2010)
country comparison to the world: 9
[see also: Military expenditures country ranks ]